1. Field of the Invention
The present invention relates to wireless communication systems and, particularly, to methods and systems for controlling handoffs in a wireless communication system.
2. Description of the Related Art
Generally speaking, wireless communication systems operate by wirelessly transmitting voice or data signals between various base stations and mobile wireless devices, such as, for example, wireless telephones and Personal Digital Assistants (PDAs).
Wireless signals may be subjected to different geographical and environmental conditions that affect signal strength. For example, multipath propagation, where both an original signal and multiple reflections of that signal are received, can cause various problems, such as echoing and signal cancellation. The former results in deceptively high measurements of received signal power while the latter results in deceptively low measurements.
Environmental conditions such as rain, humidity, wind, and temperature may also affect the medium over which signals propagate from a transmitting device to a receiver, thus affecting signal quality.
In conventional wireless communication systems, base stations determine whether a mobile wireless device should be handed off from a “serving” base station to another base station based on signal strength measurements. However, due to the geographical and environmental conditions discussed above, the measured signal strength at each base station can be a deceptive indicator of service quality. For example, base station measurements may show an unrealistically high signal strength based on multipath reflections of previous signals being aggregated with currently received signals. Disadvantageously, such deceptive signal strength measurements can cause unnecessary handoffs, or cause the mobile device to be handed off to a suboptimal base station resulting in an increased rate of calls being dropped.